UC San Diego

Corticobasal degeneration (CBD) is a clinically heterogeneous tauopathy, which has overlapping clinicopathologic and genetic characteristics with progressive supranuclear palsy (PSP). This study aimed to elucidate whether transactive response DNA-binding protein of 43 kDa (TDP-43) pathology contributes to clinicopathologic heterogeneity of CBD. Paraffin-embedded sections of the midbrain, pons, subthalamic nucleus, and basal forebrain from 187 autopsy-confirmed CBD cases were screened with immunohistochemistry for phospho-TDP-43. In cases with TDP-43 pathology, additional brain regions (i.e., precentral, cingulate, and superior frontal gyri, hippocampus, medulla, and cerebellum) were immunostained. Hierarchical clustering analysis was performed based on the topographical distribution and severity of TDP-43 pathology, and clinicopathologic and genetic features were compared between the clusters. TDP-43 pathology was observed in 45% of CBD cases, most frequently in midbrain tegmentum (80% of TDP-43-positive cases), followed by subthalamic nucleus (69%). TDP-43-positive CBD was divided into TDP-limited (52%) and TDP-severe (48%) by hierarchical clustering analysis. TDP-severe patients were more likely to have been diagnosed clinically as PSP compared to TDP-limited and TDP-negative patients (80 vs 32 vs 30%, P < 0.001). The presence of downward gaze palsy was the strongest factor for the antemortem diagnosis of PSP, and severe TDP-43 pathology in the midbrain tectum was strongly associated with downward gaze palsy. In addition, tau burden in the olivopontocerebellar system was significantly greater in TDP-positive than TDP-negative CBD. Genetic analyses revealed that MAPT H1/H1 genotype frequency was significantly lower in TDP-severe than in TDP-negative and TDP-limited CBD (65 vs 89 vs 91%, P < 0.001). The homozygous minor allele frequencies in GRN rs5848 and TMEM106B rs3173615 were not significantly different between the three groups. In conclusion, the present study indicates that CBD with severe TDP-43 pathology is a distinct clinicopathologic subtype of CBD, characterized by PSP-like clinical presentations, severe tau pathology in the olivopontocerebellar system, and low frequency of MAPT H1 haplotype.